For many employers, your number of years in the field is flexible, so long as you have the equivalent skills and results to prove your experience. This nuanced question tests your experience level by allowing you to explore this nuance with them. They're presenting you with an opportunity to pitch yourself. Take some time to consider how you'd rate your skill level versus your tenure in your field. Talk to the interviewer about your major career successes to demonstrate your experience, confidence, and leadership potential. Exhibit pride in how far you've come, and discuss what you achieved to get here and why the timing is right for you to pursue this opportunity.